Effect of Heat Input on the Microstructure and Properties of Dissimilar Weld Joint Between Incoloy 28 and Superaustenitic Stainless Steel

doi:10.1007/s40195-014-0058-y

Abstract

Abstract:

This work focuses on studying the effect of welding heat input within the range from 1 to 5 kJ/mm on the microstructure and the corresponding mechanical and corrosion properties of dissimilar joint between superaustenitic stainless steel (UNS S31254) and Incoloy 28 (UNS N08028). The two materials were butt-welded with ER NiCrMo3. The metallurgical changes associated with welding of SASS and Incoloy 28 were studied using optical microscope, SEM, and EDX. The mechanical and corrosion properties were investigated using tensile test, Vickers hardness test, and pitting and crevice corrosion tests. The weld metal microstructure showed precipitates with needle-like shape at 3 and 5 kJ/mm. Also, the microstructure showed unmixed zone (UMZ) at the fusion line of both SASS and Incoloy 28 sides at all the investigated heat inputs. The Mo microsegregation within UMZ at Incoloy 28 side increased as the heat input increased from 1 to 5 kJ/mm but that in SASS increased with increasing heat input from 1 to 3 kJ/mm and then decreased with increasing from 3 to 5 kJ/mm. The ultimate tensile strengths for all specimens at all the investigated heat inputs are acceptable. The average hardness noticeably changed in weld metal as the heat input increased from 1 to 5 kJ/mm. Other zones such as HAZ or UMZ did not demonstrate marked changes in the average hardness. The pitting and crevice corrosion rates of the weld joint were found significant at 1 and 3 kJ/mm but insignificant at 5 kJ/mm according to ASTM G48.

Key words: Superaustenitic, Incoloy 28, Welding, Heat input, Unmixed zone, Microsegregation, Corrosion

M. S. Abdel Rahman, N. A. Abdel Raheem, M. R. El Koussy. Effect of Heat Input on the Microstructure and Properties of Dissimilar Weld Joint Between Incoloy 28 and Superaustenitic Stainless Steel[J]. Acta Metallurgica Sinica (English Letters), 2014, 27(2): 259-266.

Figures/Tables 10

Table 1 The chemical composition (wt%) of base metals and filler metal

Material	C	Si	Mn	P	S	Cr	Mo	Ni	Cu	Fe	N	Nb
SASS (S31254)	0.01	0.47	0.46	0.023	0.001	19.65	6.01	18.0	0.64	Bal.	0.21	0.031
Incoloy 28 (N08028)	0.02	0.43	1.87	0.02	0.001	26.61	3.23	30.2	0.9	Bal.	0.05	0.01
ER NiCrMo3	0.01	0.08	0.35	0.01	0.004	21.2	9.1	Bal.	0.36	3.22	…	3.42

Table 2 The welding parameters of SASS and Incoloy 28 dissimilar welds

Voltage (V)	Current (A)	Speed (mm/s)	Heat input (kJ/mm)
15	60	0.87 ± 0.09	1.04 ± 0.1
16	80	0.43 ± 0.01	2.97 ± 0.05
17	100	0.33 ± 0.01	5.10 ± 0.2

Fig. 1 The microstructure of the base metal of SASS and Incoloy 28

Fig. 2 The effect of heat input on the microstructure of weld metal of dissimilar weld joints a–c. SEM photograph for the precipitate and the semiquantitative analysis of spectrum d

Fig. 3 The effect of heat input on the microstructure of HAZ and UMZ of dissimilar weld joints

Fig. 4 SEM photographs for the WM, UMZ, and HAZ of joint welded with heat input 1, 3, 5 kJ/mm and elements distributions through line AB: a, c, e Incoloy 28; b, d, f SASS

Fig. 5 The effect of the heat input on the Mo content at dendrite core and interdendrite spacing of UMZ at Incoloy 28 and SASS sides of the weld joint a, on the ratio of Mo content in interdendrite spacing to that in dendrite core b

Fig. 6 Effect of the heat input on the hardness distribution of dissimilar weld joint between Incoloy 28 and SASS

Fig. 7 Effect of the heat input on the pitting a–c and crevice d–f corrosion of dissimilar welded joint between Incoloy 28 and SASS. According to G48, the weight loss corrosion rate larger than or equal to 0.0001 g/cm2 is significant

Table 3 Effect of heat input on the ultimate tensile strength of the weld joints

Heat input (kJ/mm)	Ultimate tensile strength (MPa)
Heat input (kJ/mm)	Specimen 1	Specimen 2	Specimen 3	Average
1	680	672	658	670 ± 11
3	684	682	700	689 ± 10
5	717	739	730	729 ± 11

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